Temperature and pressure are typcially measured using temperature or pressure responsive probes located at a region of interest, such as at ground based meteorological installations or on aircraft. Applications of such direct measurement techniques are limited to only accessible regions of the atmosphere, and further could tend to interfere with the accuracy of the reading due to proximity of the measurement probe. There accordingly exists a need to provide remote pressure and temperature measurements.
Radiometric techniques have been applied to remote temperature measurement. In accordance with one technique, a tunable radiometer is made responsive to signals received in a predetermined portion of the millimeter frequency band to determine the power level of received signals at selectable frequencies within the band. The signals emanate from atmospheric molecules at power levels proportional to temperature. Various approaches are taken to determine air temperature in a predetermined volume of the atmosphere using techniques such as correlating the frequency to which the radiometer is tuned with air volume length since the distance through the atmosphere that radiation from gas molecules can travel is a function of frequency due to the frequency dependent absorption characteristics of atmospheric gases. As a practical matter, passive remote sensing techniques of this type obtain temperature measurements with vertical resolutions on only the order of a scale height with temperature accuracy of only 2.degree.-3.degree. C.
Infrared and microwave radiometers are currently providing vertical temperature profile information from satellites. This information has sufficient accuracy to enable climate modeling and weather forecasting only in the midtroposphere while exhibiting accuracies to only about 3.degree. C. at the surface and tropopause. Further, passive radiometric techniques of the type currently being used in satellite based metereological research provide temperature as a function of pressure and thus require a reference altitude pressure to obtain a height profile. Currently, this information is typically obtained from forecasts since it could not heretofore be obtained from a satellite. No techniques, active or passive, for remotely measuring atmospheric pressure are known.
It is accordingly an object of the present invention to provide a method of and apparatus for remotely measuring temperature and/or pressure of a gas.
A further object is to provide a method of and apparatus for making remote measurements of temperature and/or pressure of air.